1. Field of the Invention
This invention relates to a process for preparing an alcohol by hydrating an olefin in the presence of a catalyst. More particularly, it relates to a process for reacting an olefin with water to prepare a corresponding alcohol in the presence of a crystalline aluminosilicate, as a catalyst, which is selected from offretite, ferrierite and erionite.
2. Description of the Prior Art
A process for hydrating an olefin, especially a lower olefin such as ethylene, propylene or butene, to prepare a corresponding alcohol such as ethanol, propanol or butanol, is industrially important. Various processes are known for this hydration reaction, but a process using a mineral acid such as sulfuric acid or phosphoric acid is industrially adopted.
A vapor phase process using a phosphoric acid supported on a silica gel is industrially adopted for preparing ethanol by the hydration of ethylene. In this process, however, phosphoric acid supported on the silica gel is eluted whereby the activity is degraded. Accordingly, it is necessary to perpetually add phosphoric acid. Therefore, problems arise in connection with the treatment of the discharged waste liquid and the corrosion of the material of equipment. Furthermore, a large quantity of energy is necessary for recovery of unreacted ethylene or separation and purification of the produced ethanol because the conversion of ethylene is low.
A liquid phase process using sulfuric acid is widely adopted on the hydration of propylene or butenes, industrially. However, in this process, a large quantity of energy is necessary for hydrolysis of a sulfuric acid ester once formed and concentration and regeneration of the diluted aqueous sulfuric acid solution and equipment is violently corroded by the acid at high temperatures.
From equilibrium considerations, it is preferred that the hydration of olefins be carried out at a low temperature under a high pressure, and ordinarily, these reaction conditions provide high conversions of olefins to alcohols. However, it is necessary to obtain an industrially satisfactory rate of reaction, and practically, severe conditions of high temperatures and high pressures are adopted for obtaining such a high rate of reaction. For these reasons, it is eagerly desired to develop a highly active solid acid catalyst for the hydration of olefins, which is capable of reducing the consumption of energy and not causing corrosion of equipment or other trouble.
Attempts have heretofore been made to use solid catalysts for the hydration of olefins. For example, there have been proposed processes using complex oxides composed of silica, alumina, zirconia, titanium oxide, molybdenum oxide and tungsten oxide, metal phosphates such as aluminum phosphate and zirconium phosphate, and crystalline aluminosilicates called "zeolites" such as mordenite and Y type zeolite. However, these catalysts possess a low activity and the activity is gradually degraded when the reaction is carried out at a high temperature.
As the process using as a catalyst a crystalline aluminosilicate, which is relevant to the process of the present invention, there can be mentioned a process using a ZSM-5 type zeolite, which is disclosed in Japanese Unexamined Patent Publication No. 57-70,828.
A zeolite has a peculiar fine pore structure based on its characteristic crystal structure, and since it has a strong solid acidity, it is expected that it will probably be used as a catalyst. We examined various zeolites in connection with their activities for hydration of olefins, and it was confirmed that when zeolites heretofore proposed are used as the catalyst, the activity is not satisfactorily high, large quantities of by-products such as olefin oligomers, aldehydes and ketones are ordinarily formed, the selectivity to the intended alcohol is low and the activity is reduced by coking in many cases.